Rechargeable lithium batteries use materials capable of reversibly intercalating or deintercalating lithium ions in the positive and negative electrodes, and include organic electrolyte solutions or polymer electrolytes between the positive and negative electrodes. Rechargeable lithium batteries generate electrical energy by oxidation/reduction reactions during the intercalation/deintercalation of lithium ions at the positive and negative electrodes.
For positive active materials, composite metal oxides, such as LiCoO2, LiMn2O4, LiNiO2, LiNi1-xCoxO2 (0<x<1), LiMnO2, etc., have been researched.
Conventionally, lithium metals have been used as the negative active materials for rechargeable lithium batteries. However, when using lithium metal, dendrites form causing a short circuit in the battery which can lead to explosion. Therefore, carbonaceous materials, such as amorphous carbon, crystalline carbon, etc., have recently been used in place of lithium metals as the negative active materials. However, such carbonaceous materials increase irreversible capacity by 5 to 30% during the first several cycles, which wastes lithium ions and prevents at least one active material from being fully charged and discharged. Therefore, carbonaceous materials impart disadvantageous energy densities.
In addition, it is known that metal negative active materials such as Si, Sn, etc., which supposedly have high capacities, also impart irreversible capacity characteristics. Further, tin oxide has been investigated as an alternative to carbonaceous negative active materials. However, the metal is included in the negative active material in an amount of 30% or less, thereby decreasing the initial coulomb efficiency. Further, lithium is continuously intercalated and deintercalated, thereby generating lithium-metal alloys and remarkably decreasing capacity. In addition, the capacity retention rate remarkably deteriorates after repeating 150 charge and discharge cycles. As a result, these negative active materials are not commercially viable. Accordingly, much research has been conducted to improve these characteristics.